The present invention relates in general to the manufacturing of drawn sheet metal parts in a press, and, more particularly, relates to an apparatus and method for trimming the circumference of a drawn part as a result of vertical movement of the press.
Sheet metal parts have been made with dies that run in presses for decades. Dies are typically comprised of a fixed lower die portion and an upper punch portion which is reciprocally movable with respect to the lower die portion. The upper punch portion is typically connected to the ram of a press. The ram is generally slidably mounted within rails along either side of a press which constrain the ram to vertical movement therein. In addition, a motor having an output shaft is provided on the press. The output shaft typically has a distal end provided with a concentrically mounted plate thereon which, in turn, is connected to an eccentric crankshaft. Further, the ram has one end mounted to an upper surface of the punch portion of the die and on opposite end having a bearing which is journaled to the crankshaft. Thus, as rotational motion is imparted to the output shaft by the motor, the crankshaft is rotated as well and traces a circular path. As a result, the ram, in conjunction with the upper punch portion of the die, is moved reciprocally within the rails with respect to the lower die portion.
Each rotation of the output shaft of the motor is relative to the xe2x80x9cstrokexe2x80x9d of the machine and ranges between 0 and 360 degrees. Thus, the point at which the eccentric portions of the crankshaft are located at the uppermost vertical position with respect to the plate is referred to as the 0 degree position or xe2x80x9ctop dead centerxe2x80x9d (TDC). At TDC, the upper punch portion of the die is positioned the greatest extent above the lower die portion. The point at which the eccentric portions of the crankshaft are located adjacent to the lowermost vertical position with respect to the plate is referred to as the 180 degree position or xe2x80x9cbottom dead centerxe2x80x9d (BDC). In the 180 degree position, the upper punch portion is positioned adjacent to the lower die portion and is the position whereby the forming operations are performed on the part. The distance the ram travels from TDC to BDC is referred to as the xe2x80x9cstrokexe2x80x9d of the press.
Dies have been developed that pierce, form, draw, and trim sheet metal to produce a part of a desired shape. As the state of the art has progressed, dies have been developed to combine some of these operations in a single die. Other dies, called progressive dies, have been developed that combine several die stations on a common base to be operated within a single press. A progressive die performs a series of fundamental sheet metal operations at two or more stations in the die during each press stroke. These simultaneous operations produce a part from a strip of material that moves through each die. Each working station performs one or more die operations such as shaping, piercing or drawing the strip of stock material, but the strip must move from the first station through each succeeding station in a substantially linear path to produce a complete part.
The advancement of sheet metal dies has also seen the development of dies which are capable of trimming a part, i.e., removing excess material from a completed part, in a direction substantially perpendicular to the stroke of the press. In these operations, cams or other actuating means are typically employed to impart movement of at least one of the trimming surfaces. Unfortunately, the cams typically actuate a large portion of the die while significantly moving the entire part relative to the die or press. Thus, incorporation of cam trim dies in a progressive die is substantially impossible since the strip of material constrains movement of the part and the strip of material is moving in a linear path. Moreover, excess movement of the strip may affect the operations in other stations in the progressive die. Additionally, the large movement is difficult in progressive dies because of the speed of operation. Progressive dies are often operated in presses running at between 30 and 200 strokes per minute. Often, there is simply not enough time for a large movement of the tooling in a single press stroke.
Other cam trim dies have been developed which require less movement of the die or part. However, these cam trim dies typically have complex actuating means and require more time to index the trim surfaces or elements, and are thus not practical in many progressive dies. As stated above, progressive dies are often operated at between 30 and 200 strokes per minute. As the speed of the press increases, the speed of the actuating means proportionally increases. Often, the speed of the press does not allow for the use complex trim actuating means due to time constraints. Further, to attain these high press speeds, the stroke length of the press must be limited. Adaption of both complex actuating means and dies with large movements to progressive dies can be problematic when stroke lengths are relatively small.
In view of the above, there is a long felt but unsolved need for a sheet metal trim die that avoids the above-mentioned deficiencies of the prior art and provides a simple sheet metal die which is capable of trimming the entire circumference of a drawn part in a direction which is oriented perpendicular to the operation of a reciprocating press while limiting movement of the part.
Accordingly, it is an object of the present invention to provide a sheet metal die which is capable of trimming the entire circumference of a drawn part in a single stroke of a press which imparts insignificant motion to the part. The limited motion of the part may facilitate use of the trim die in combination with various transfer mechanisms to deliver the part to and from the die or as one of numerous stations in a progressive die.
Another object of the present invention is to provide a trim die in which the moving trim surfaces are contained within a portion of the die itself. The movement of an internal portion of the die obviates the need for movement of large portions of the die and, thus, provides the benefit of minimal space requirements, increased operating speeds, and decreased stroke length requirements.
Yet another aspect of the present invention is to provide a trim actuating mechanism which can be used in one of a plurality of stations of a progressive die to trim a circumference of a drawn part. The achievement of the objects mentioned above facilitate the use of the present invention in a progressive die. More specifically, the use of the present invention in a progressive die may eliminate additional stations or operations currently required in progressive dies for trimming the circumference of a drawn part. For example, it is commonly necessary for a progressive die to trim excess material from a drawn part in a direction parallel to the motion of the press. It then becomes necessary to perform a wiping operation to bring the flange created by trimming back into alignment with the drawn edge. The use of the present invention would make the wiping operation unnecessary.
These and other objects of the present invention are fulfilled by providing a die assembly including a punch plate having a plurality of cam punches interconnected thereto, the plurality of cam punches each having a cam lobe. Further, a die plate is provided which has a part recess sized to receive at least a portion of the drawn part, the upper circumference of the part recess forming an exterior trim edge, a stripper plate sub-assembly (hereinafter the xe2x80x9cstripper platexe2x80x9d) moveably interconnected to the punch plate and having a plurality of apertures for receiving the cam punches, and a trim plate horizontally moveably mounted in the stripper plate and having a plurality of lateral sides and a trim punch. The cam punches move the trim plate horizontally with respect to a longitudinal axis of the cam punches by engaging the lateral sides of the trim plate with the cam lobes as the stripper plate is moved toward the punch plate. The excess material is trimmed from at least a portion of the circumference of the drawn part by the movement of the trim punch relative to the exterior trim edge.
Thus, in one aspect of the present invention, a method adapted for progressively forming and trimming a part in a reciprocating die press from a strip of stock material is provided comprising the steps of introducing a strip of stock material into the reciprocating press having one or more progressive stations in series to draw, shape, pierce or otherwise form a portion of the strip of stock material; cycling the press to perform at least one operation on said strip of stock material, wherein a portion of the strip of stock material is drawn, shaped, pierced or otherwise formed into a desired shape; advancing the desired shape into a trimming station which is operably interconnected to the press; and trimming any excess of the strip of stock material from the desired shape as the press reciprocates.
Additional advantages of the present invention will become readily apparent from the following discussion, particularly when taken together with the accompanying drawings.